#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
ambari_jinja2.sandbox
~~~~~~~~~~~~~~

Adds a sandbox layer to Jinja as it was the default behavior in the old
Jinja 1 releases.  This sandbox is slightly different from Jinja 1 as the
default behavior is easier to use.

The behavior can be changed by subclassing the environment.

:copyright: (c) 2010 by the Jinja Team.
:license: BSD.
"""

import operator
from ambari_jinja2.runtime import Undefined
from ambari_jinja2.environment import Environment
from ambari_jinja2.exceptions import SecurityError
from ambari_jinja2.utils import (
  FunctionType,
  MethodType,
  TracebackType,
  CodeType,
  FrameType,
  GeneratorType,
)


#: maximum number of items a range may produce
MAX_RANGE = 100000

#: attributes of function objects that are considered unsafe.
UNSAFE_FUNCTION_ATTRIBUTES = set(
  ["func_closure", "func_code", "func_dict", "func_defaults", "func_globals"]
)

#: unsafe method attributes.  function attributes are unsafe for methods too
UNSAFE_METHOD_ATTRIBUTES = set(["im_class", "im_func", "im_self"])


import warnings

# make sure we don't warn in python 2.6 about stuff we don't care about
warnings.filterwarnings(
  "ignore", "the sets module", DeprecationWarning, module="ambari_jinja2.sandbox"
)

from collections import deque

_mutable_set_types = (set,)
_mutable_mapping_types = (dict,)
_mutable_sequence_types = (list,)


# on python 2.x we can register the user collection types
try:
  from UserDict import UserDict, DictMixin
  from collections import UserList

  _mutable_mapping_types += (UserDict, DictMixin)
  _mutable_set_types += (UserList,)
except ImportError:
  pass

# if sets is still available, register the mutable set from there as well
try:
  from sets import Set

  _mutable_set_types += (Set,)
except ImportError:
  pass

#: register Python 2.6 abstract base classes
try:
  try:
    from collections.abc import MutableSet, MutableMapping, MutableSequence
  except ImportError:
    from collections import MutableSet, MutableMapping, MutableSequence

  _mutable_set_types += (MutableSet,)
  _mutable_mapping_types += (MutableMapping,)
  _mutable_sequence_types += (MutableSequence,)
except ImportError:
  pass

_mutable_spec = (
  (
    _mutable_set_types,
    frozenset(
      [
        "add",
        "clear",
        "difference_update",
        "discard",
        "pop",
        "remove",
        "symmetric_difference_update",
        "update",
      ]
    ),
  ),
  (
    _mutable_mapping_types,
    frozenset(["clear", "pop", "popitem", "setdefault", "update"]),
  ),
  (
    _mutable_sequence_types,
    frozenset(["append", "reverse", "insert", "sort", "extend", "remove"]),
  ),
  (
    deque,
    frozenset(
      [
        "append",
        "appendleft",
        "clear",
        "extend",
        "extendleft",
        "pop",
        "popleft",
        "remove",
        "rotate",
      ]
    ),
  ),
)


def safe_range(*args):
  """A range that can't generate ranges with a length of more than
  MAX_RANGE items.
  """
  rng = range(*args)
  if len(rng) > MAX_RANGE:
    raise OverflowError("range too big, maximum size for range is %d" % MAX_RANGE)
  return rng


def unsafe(f):
  """
  Mark a function or method as unsafe::

      @unsafe
      def delete(self):
          pass
  """
  f.unsafe_callable = True
  return f


def is_internal_attribute(obj, attr):
  """Test if the attribute given is an internal python attribute.  For
  example this function returns `True` for the `func_code` attribute of
  python objects.  This is useful if the environment method
  :meth:`~SandboxedEnvironment.is_safe_attribute` is overriden.

  >>> from ambari_jinja2.sandbox import is_internal_attribute
  >>> is_internal_attribute(lambda: None, "func_code")
  True
  >>> is_internal_attribute((lambda x:x).func_code, 'co_code')
  True
  >>> is_internal_attribute(str, "upper")
  False
  """
  if isinstance(obj, FunctionType):
    if attr in UNSAFE_FUNCTION_ATTRIBUTES:
      return True
  elif isinstance(obj, MethodType):
    if attr in UNSAFE_FUNCTION_ATTRIBUTES or attr in UNSAFE_METHOD_ATTRIBUTES:
      return True
  elif isinstance(obj, type):
    if attr == "mro":
      return True
  elif isinstance(obj, (CodeType, TracebackType, FrameType)):
    return True
  elif isinstance(obj, GeneratorType):
    if attr == "gi_frame":
      return True
  return attr.startswith("__")


def modifies_known_mutable(obj, attr):
  """This function checks if an attribute on a builtin mutable object
  (list, dict, set or deque) would modify it if called.  It also supports
  the "user"-versions of the objects (`sets.Set`, `UserDict.*` etc.) and
  with Python 2.6 onwards the abstract base classes `MutableSet`,
  `MutableMapping`, and `MutableSequence`.

  >>> modifies_known_mutable({}, "clear")
  True
  >>> modifies_known_mutable({}, "keys")
  False
  >>> modifies_known_mutable([], "append")
  True
  >>> modifies_known_mutable([], "index")
  False

  If called with an unsupported object (such as unicode) `False` is
  returned.

  >>> modifies_known_mutable("foo", "upper")
  False
  """
  for typespec, unsafe in _mutable_spec:
    if isinstance(obj, typespec):
      return attr in unsafe
  return False


class SandboxedEnvironment(Environment):
  """The sandboxed environment.  It works like the regular environment but
  tells the compiler to generate sandboxed code.  Additionally subclasses of
  this environment may override the methods that tell the runtime what
  attributes or functions are safe to access.

  If the template tries to access insecure code a :exc:`SecurityError` is
  raised.  However also other exceptions may occour during the rendering so
  the caller has to ensure that all exceptions are catched.
  """

  sandboxed = True

  def __init__(self, *args, **kwargs):
    Environment.__init__(self, *args, **kwargs)
    self.globals["range"] = safe_range

  def is_safe_attribute(self, obj, attr, value):
    """The sandboxed environment will call this method to check if the
    attribute of an object is safe to access.  Per default all attributes
    starting with an underscore are considered private as well as the
    special attributes of internal python objects as returned by the
    :func:`is_internal_attribute` function.
    """
    return not (attr.startswith("_") or is_internal_attribute(obj, attr))

  def is_safe_callable(self, obj):
    """Check if an object is safely callable.  Per default a function is
    considered safe unless the `unsafe_callable` attribute exists and is
    True.  Override this method to alter the behavior, but this won't
    affect the `unsafe` decorator from this module.
    """
    return not (
      getattr(obj, "unsafe_callable", False) or getattr(obj, "alters_data", False)
    )

  def getitem(self, obj, argument):
    """Subscribe an object from sandboxed code."""
    try:
      return obj[argument]
    except (TypeError, LookupError):
      if isinstance(argument, str):
        try:
          attr = str(argument)
        except:
          pass
        else:
          try:
            value = getattr(obj, attr)
          except AttributeError:
            pass
          else:
            if self.is_safe_attribute(obj, argument, value):
              return value
            return self.unsafe_undefined(obj, argument)
    return self.undefined(obj=obj, name=argument)

  def getattr(self, obj, attribute):
    """Subscribe an object from sandboxed code and prefer the
    attribute.  The attribute passed *must* be a bytestring.
    """
    try:
      value = getattr(obj, attribute)
    except AttributeError:
      try:
        return obj[attribute]
      except (TypeError, LookupError):
        pass
    else:
      if self.is_safe_attribute(obj, attribute, value):
        return value
      return self.unsafe_undefined(obj, attribute)
    return self.undefined(obj=obj, name=attribute)

  def unsafe_undefined(self, obj, attribute):
    """Return an undefined object for unsafe attributes."""
    return self.undefined(
      "access to attribute %r of %r "
      "object is unsafe." % (attribute, obj.__class__.__name__),
      name=attribute,
      obj=obj,
      exc=SecurityError,
    )

  def call(__self, __context, __obj, *args, **kwargs):
    """Call an object from sandboxed code."""
    # the double prefixes are to avoid double keyword argument
    # errors when proxying the call.
    if not __self.is_safe_callable(__obj):
      raise SecurityError(f"{__obj!r} is not safely callable")
    return __context.call(__obj, *args, **kwargs)


class ImmutableSandboxedEnvironment(SandboxedEnvironment):
  """Works exactly like the regular `SandboxedEnvironment` but does not
  permit modifications on the builtin mutable objects `list`, `set`, and
  `dict` by using the :func:`modifies_known_mutable` function.
  """

  def is_safe_attribute(self, obj, attr, value):
    if not SandboxedEnvironment.is_safe_attribute(self, obj, attr, value):
      return False
    return not modifies_known_mutable(obj, attr)
